Herpes simplex viruses are endemic in the population and are responsible for a variety of clinical diseases some of which are life threatening, especially in immunocompromised individuals or in newborns. The processes of viral genome maturation and encapsidation appear to be a multistep operation involving the function of at least eight viral gene products as revealed by the analysis of viral mutants. These viral genes (UL6, UL12, UL15, ULI7, UL25, UL28, UL32 and UL33) are well conserved within the herpesvirus family indicating that they likely play important roles in the viral life cycle. The objective of this proposal is to provide a better understanding of the events of genome processing and packaging through genetic and biochemical analysis. The first aim is to determine the role of UL15 and UL28 in cleavage and packaging. We plan to test the hypothesis that these proteins encode the putative terminase/translocase. To this end we will attempt to purify a soluble UL15/UL28 protein complex and test biochemically for functions expected of a terminase. We also will extend our genetic analysis of these two gene products. The second aim is to further characterize the roles of UL6 and UL32. Preliminary evidence suggests that UL6 may act as a portal protein and the UL32 is required for capsids to localize correctly in infected cells. These assignments will be tested by genetic analysis. The third aim is to continue the identification of the cleavage and packaging proteins that are associated with procapsids isolated from cells infected with mutants blocked at various stages in the encapsidation process. It is anticipated that this type of analysis will provide additional clues about the roles of these proteins. We also plan to examine capsid localization during infection to characterize the spatial organization of the encapsidation process. Long term aims include the development of an in vitro cleavage and packaging reaction. It is anticipated that this proposal will not only enhance our understanding of the mechanisms of genome maturation and encapsidation but may also lead to the development of novel strategies for antiviral therapy.